One problem associated with known pulse combustor apparatus of the type having a Combustor tube with open ends, i.e., a "Rijke" tube, is that it can be difficult to burn solid fuels, such as coal, therein efficiently and effectively. For example, if coal is burned in a Rijke tube using overfeed fuel bed burning, in which coal is added above a grate and air for combustion is introduced from beneath the grate, the combustor apparatus can become choked or clogged rather quickly. This clogging of the combustor apparatus is caused in part by agglomeration of the coal and in part by accumulation of ash. Agglomeration of the coal is a result of a softening or melting of some of the constituents of the coal which causes the coal particles to stick together. Agglomeration is detrimental to complete and efficient combustion in that some amount of coal inside of the agglomerated clump is not exposed to combustion air, but rather is insulated from contacting combustion air. Thus, unburned coal can accumulate on the grate in this way until the combustor tube is partially or completely clogged. The agglomerated coal also inhibits the passing of combustion air through the bed.
Ash accumulation can also act to clog the combustor tube. Ash is the inorganic residue resulting from the burning of coal and generally consists mainly of silica, alumina, ferric oxide, and lime, along with smaller amounts of other compounds. Depending upon the source of the coal, ash content can be as little as 3% of the unburned coal or more than 25%. As the coal burns, ash melts and seals over a portion of the free carbon, thereby reducing the amount of carbon that can be burned. As the combustion of coal continues over time, the ash continues to accumulate and must be removed from the fuel bed. For example, in some furnaces, though not in known Rijke pulse combustors, coal is carried into a combustion chamber from one side by a conveyor and after the coal has been burned on &he conveyor, the resulting ash is carried out of the combustion chamber by the same conveyor.
Another problem with burning solid fuels, such as coal, in a Rijke Pulse combustor is that an undesirably large amount of pollution in the form of NO.sub.x is generated and emitted. The emission of NO.sub.x can present a more difficult problem when burning some solid fuels, such as coal, than when burning gaseous or liquid fuels. This is so because many solid fuels contain small but significant amounts of bonded nitrogen. For example, coal typically contains approximately 1% to 1.5% nitrogen. During combustion, this fuel-borne nitrogen can combine with oxygen present in the combustion air to form NO.sub.x Indeed, in the combustion of coal in typical known apparatus, greater than 80% of the NO.sub.x formed is a result of fuel-borne nitrogen and less than 20% of the NO.sub.x is formed by thermal processes acting on the nitrogen component of the combustion air.
Another problem associated with burning coal is the emission of sulphur dioxide (SO.sub.2) as a result of the sulphur content of the coal.
Thus, it can be seen that a need exists for a pulse combustor apparatus which can burn solid fuels, such as coal, effectively and efficiently while avoiding clogging and choking due to ash accumulation and agglomeration, and while minimizing the output of NO.sub.x and SO.sub.2. It is to the provision of such therefore that the present invention is primarily directed.